linux-kernel - [PATCH] lib/flex_proportions.c: Use abs() when percpu

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Date:   Mon, 17 May 2021 23:53:06 +0800
From:   Chi Wu <wuchi.zero@...il.com>
To:     akpm@...ux-foundation.org
Cc:     jack@...e.cz, linux-kernel@...r.kernel.org, tan.hu@....com.cn,
        Chi Wu <wuchi.zero@...il.com>
Subject: [PATCH] lib/flex_proportions.c: Use abs() when percpu_counter is negative.

The value of percpu_counter_read() may become negative after
running percpu_counter_sum() in fprop_reflect_period_percpu().
The value of variable 'num' will be zero in fprop_fraction_percpu()
when using percpu_counter_read_positive(), but if using the abs of
percpu_counter_read() will be close to the correct value.

Signed-off-by: Chi Wu <wuchi.zero@...il.com>
---
 lib/flex_proportions.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c
index 451543937524..3ac79ca2c441 100644
--- a/lib/flex_proportions.c
+++ b/lib/flex_proportions.c
@@ -147,7 +147,7 @@ void fprop_fraction_single(struct fprop_global *p,
 		seq = read_seqcount_begin(&p->sequence);
 		fprop_reflect_period_single(p, pl);
 		num = pl->events;
-		den = percpu_counter_read_positive(&p->events);
+		den = abs(percpu_counter_read(&p->events));
 	} while (read_seqcount_retry(&p->sequence, seq));
 
 	/*
@@ -209,7 +209,7 @@ static void fprop_reflect_period_percpu(struct fprop_global *p,
 			val = percpu_counter_sum(&pl->events);
 
 		percpu_counter_add_batch(&pl->events,
-			-val + (val >> (period-pl->period)), PROP_BATCH);
+			-val + (val >> (period - pl->period)), PROP_BATCH);
 	} else
 		percpu_counter_set(&pl->events, 0);
 	pl->period = period;
@@ -234,8 +234,8 @@ void fprop_fraction_percpu(struct fprop_global *p,
 	do {
 		seq = read_seqcount_begin(&p->sequence);
 		fprop_reflect_period_percpu(p, pl);
-		num = percpu_counter_read_positive(&pl->events);
-		den = percpu_counter_read_positive(&p->events);
+		num = abs(percpu_counter_read(&pl->events));
+		den = abs(percpu_counter_read(&p->events));
 	} while (read_seqcount_retry(&p->sequence, seq));
 
 	/*
-- 
2.17.1